Implemented cipher rekeying

noise/builder.py
- Added methods for rekeying cipherstates
- Added method for getting handshake hash (for channel binding)

noise/functions.py
- Added default rekey behavior and set it for AESGCM and ChaCha20

noise/constants.py
- Added MAX_NONCE

noise/state.py
- Added rekey method to CipherState
- Removed writing to noise_protocol instance in SymmetricState.
NoiseProtocol fills the appropriate field by taking the data from
HandshakeState now.

noise/builder.py

@@ -69,11 +69,11 @@ class NoiseBuilder(object):
         self.noise_protocol.initiator = False
         self._next_fn = self.read_message
 
-    def set_keypair_from_private_bytes(self, keypair, private_bytes: bytes):
+    def set_keypair_from_private_bytes(self, keypair: Keypair, private_bytes: bytes):
         self.noise_protocol.keypairs[_keypairs[keypair]] = \
             self.noise_protocol.dh_fn.keypair_cls.from_private_bytes(private_bytes)
 
-    def set_keypair_from_public_bytes(self, keypair, private_bytes: bytes):
+    def set_keypair_from_public_bytes(self, keypair: Keypair, private_bytes: bytes):
         self.noise_protocol.keypairs[_keypairs[keypair]] = \
             self.noise_protocol.dh_fn.keypair_cls.from_public_bytes(private_bytes)
 
@@ -129,3 +129,12 @@ class NoiseBuilder(object):
 
     def decrypt(self, data: bytes):
         return self.noise_protocol.cipher_state_decrypt.decrypt_with_ad(None, data)
+
+    def get_handshake_hash(self) -> bytes:
+        return self.noise_protocol.handshake_hash
+
+    def rekey_inbound_cipher(self):
+        self.noise_protocol.cipher_state_decrypt.rekey()
+
+    def rekey_outbound_cipher(self):
+        self.noise_protocol.cipher_state_encrypt.rekey()

noise/constants.py

@@ -16,3 +16,5 @@ TOKEN_PSK = 'psk'
 MAX_PROTOCOL_NAME_LEN = 255
 
 MAX_MESSAGE_LEN = 65535
+
+MAX_NONCE = 2 ** 64 - 1

noise/functions.py

@@ -9,7 +9,7 @@ from cryptography.hazmat.backends import default_backend
 from cryptography.hazmat.primitives.asymmetric import x25519
 from cryptography.hazmat.primitives.ciphers.aead import AESGCM, ChaCha20Poly1305
 # from cryptography.hazmat.primitives.hmac import HMAC  # Turn back on when Cryptography gets fixed
-
+from noise.constants import MAX_NONCE
 from .crypto import X448
 
 backend = default_backend()
@@ -53,10 +53,12 @@ class Cipher(object):
             self._cipher = AESGCM
             self.encrypt = self._aesgcm_encrypt
             self.decrypt = self._aesgcm_decrypt
+            self.rekey = self._default_rekey
         elif method == 'ChaCha20':
             self._cipher = ChaCha20Poly1305
             self.encrypt = self._chacha20_encrypt
             self.decrypt = self._chacha20_decrypt
+            self.rekey = self._default_rekey
         else:
             raise NotImplementedError('Cipher method: {}'.format(method))
 
@@ -85,6 +87,9 @@ class Cipher(object):
     def _chacha20_nonce(self, n):
         return b'\x00\x00\x00\x00' + n.to_bytes(length=8, byteorder='little')
 
+    def _default_rekey(self, k):
+        return self.encrypt(k, MAX_NONCE, b'', b'\x00' * 32)[:32]
+
 
 class Hash(object):
     def __init__(self, method):

noise/noise_protocol.py

@@ -1,5 +1,5 @@
 from functools import partial
-from typing import Tuple, List
+from typing import Tuple
 
 from noise.exceptions import NoiseProtocolNameError, NoisePSKError
 from noise.state import HandshakeState
@@ -133,3 +133,4 @@ class NoiseProtocol(object):
             if value:
                 kwargs[keypair] = value
         self.handshake_state = HandshakeState.initialize(self, **kwargs)
+        self.symmetric_state = self.handshake_state.symmetric_state

noise/state.py

@@ -1,6 +1,6 @@
 from typing import Union
 
-from .constants import Empty, TOKEN_E, TOKEN_S, TOKEN_EE, TOKEN_ES, TOKEN_SE, TOKEN_SS, TOKEN_PSK
+from .constants import Empty, TOKEN_E, TOKEN_S, TOKEN_EE, TOKEN_ES, TOKEN_SE, TOKEN_SS, TOKEN_PSK, MAX_NONCE
 
 
 class CipherState(object):
@@ -34,7 +34,7 @@ class CipherState(object):
         :param plaintext: bytes sequence
         :return: ciphertext bytes sequence
         """
-        if self.n == 2**64 - 1:
+        if self.n == MAX_NONCE:
             raise Exception('Nonce has depleted!')
 
         if not self.has_key():
@@ -62,6 +62,9 @@ class CipherState(object):
         self.n = self.n + 1
         return plaintext
 
+    def rekey(self):
+        self.k = self.noise_protocol.cipher_fn.rekey(self.k)
+
 
 class SymmetricState(object):
     """
@@ -87,7 +90,6 @@ class SymmetricState(object):
         # Create SymmetricState
         instance = cls()
         instance.noise_protocol = noise_protocol
-        noise_protocol.symmetric_state = instance
 
         # If protocol_name is less than or equal to HASHLEN bytes in length, sets h equal to protocol_name with zero
         # bytes appended to make HASHLEN bytes. Otherwise sets h = HASH(protocol_name).